The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. In some cases, a lack of formation pressure or the viscosity of the hydrocarbon produced from the formation (among other reasons) require the use of artificial lift systems to extract the hydrocarbon fluid from the well. One type of artificial lift system involves the use of electric submersible pumps (ESPs) to provide a motivating force for the extraction of fluid from the well.
The present disclosure relates generally to permanent downhole electrical connector systems installed onto a permanent completion use, e.g., with ESP applications. The present disclosure also relates generally to retrievable wet connector systems used in a downhole environment for, e.g., ESP applications. The present disclosure focuses on the ESP cable connections employed at the surface of such ESP applications.
ESP systems require connection to an electric power supply, which drives the motor (not specific to motor type). Conventional ESPs typically use electrical connectors that are assembled manually. These are simple plug and socket type connections, which must be fitted in a controlled environment.
In a typical ESP application (tubing deployed ESP), the electrical power is supplied to the electric motor from the surface VSD via an ESP cable. The ESP cable is installed onto the production tubing during the ESP installation and it is normally terminated in a MLE (motor lead extension) which incorporates a pothead. The pothead then is connected to the motor during the installation.
Typically, a male/female connector is employed that enables the connection between power supply and ESP to be made-up remotely, so that it is operable in the harsh conditions of an oil-well, where high pressures and temperatures are present, and the fluid filled environment may be corrosive.
With the retrievable ESP system, the ESP cable is installed onto the production tubing and the permanent completion and it is connected to the permanent downhole wet connector (fixed end). The power is then transferred to the motor through the retrievable mating wet connector (plug head) when this is deployed and connected to the downhole wet connector.
More particularly, the present disclosure relates to tubing encapsulated power cable (TEPC) used with ESP applications, and to a stress cone adapted for installation on the terminated end of the TEPC at the surface.
An extended cable may be provided to power an ESP located at a distance downhole. This cable would have to survive the incredibly harsh environment of the wellbore. To facilitate survival, various layers of insulation and coatings may surround the individual conduits providing the electricity. However, terminations of cables, such as terminating a power cable into another component such as a connector housing, present challenges in properly cutting and preparing the cable for establishing a reliable connection to another component. Improper or incorrect termination may generate unintended leak paths and corrosion due to contamination by wellbore fluid as well as creating potential concentrations of electrical stresses due to non-uniform cable cutting.
ESP power systems (ESP cables and the associated connectors and feed-throughs) are very complex, long (typically 5,000 ft) power delivery systems that must withstand very high voltages (typically 5 KVAC phase to phase) over long periods of operation (10+ years) in a high temperature, high pressure environment (producing wellbore). The insulation that provides electrical isolation within the power systems must withstand these conditions in the presence of reactive and corrosive gases and fluids (H2S, CO2, Water, chlorides, etc.) that are damaging to most insulations. In addition, ESP cables are subjected to extreme mechanical stress during installation and operation.
The industry typically uses a lead sheath or other ‘non-reactive’ barrier to provide a ‘chemical barrier’ between the wire insulation and the fluids in the wellbore. Although these barriers can be effective in isolating the insulation from the damaging fluids, they are highly susceptible to damage in that they are soft, easy to tear, and hard to terminate. ESP power system failures often occur at the termination of the protective sheath or where the sheath is not present (e.g., at connectors, splices, feed-throughs, and sites of mechanical damage to sheath).
Past attempts have been made to use a robust sheath (metallic tube instead of lead) but these have failed for several reasons. For example, traditionally, the metallic sheath of TEPC is very difficult to terminate in the field, making installation in the field impractical. Additionally, another source of failure is the voltage stress induced by the metallic sheath in high voltage applications leading to premature failure.
Typically, the ESP power delivery system is responsible for 15-35% of ESP failures. The replacement of a failed ESP system will typically cost $300 K to $15 MM, not including the cost of the lost production while the ESP system is non-operational (it can take up to one year to replace). This cost represents a huge burden on oil and gas operations.
Therefore, there continues to exist a need to provide an enhanced power delivery system that minimizes voltage stress within high voltage ESP power systems, particularly where field termination of TEPC is employed.
Applicant AccessESP UK Limited has developed new termination techniques that do not require these difficult field terminations, such as those described in, e.g., copending U.S. patent application Ser. No. 15/408,336, filed Jan. 17, 2017, Publication No. 20170204680, which is incorporated herein by reference in its entirety. Applicant has also developed improved systems and methods for cutting and preparing the cable ends for establishing a reliable connection to another component. Examples of such improvements are described in copending U.S. Provisional Patent Application Ser. No. 62/561,654, filed on Sep. 21, 2017 entitled “System and Method for Terminating Cable”, which is incorporated herein by reference in its entirety.